Radiation Therapy: The Basics

Carolyn Vachani, RN, MSN, AOCN
Abramson Cancer Center of the University of Pennsylvania
Last Modified: December 18, 2014

What is radiation therapy, and how does it work?

Tumors are made up of cells that are reproducing at abnormally high rates. Radiation therapy specifically acts against cells that are reproducing rapidly. Normal cells are programmed to stop reproducing (or dividing) when they come into contact with other cells. In the case of a tumor, this stop mechanism is missing, causing cells to continue to divide over and over. It is the DNA of the cell that makes it capable of reproducing. Radiation therapy uses high energy x-rays to damage the DNA of cells, thereby killing the cancer cells, or at least stopping them from reproducing. Radiation also damages normal cells, but because normal cells are growing more slowly, they are better able to repair this radiation damage than are cancer cells. In order to give normal cells time to heal and to reduce a patient's side effects, radiation treatments are typically given in small daily doses, five days a week, over a six-or seven-week period. It is estimated that more than 50% of cancer patients will receive radiation at some point during their treatment.

How is radiation therapy given?

Radiation therapy is considered to be a "local" therapy, meaning it treats a specific localized area of the body. This is in contrast to systemic therapies, such as chemotherapy, which travel throughout the body. There are two main types of radiation therapy: external radiation therapy, where a beam of radiation is directed from outside the body, and internal radiation therapy, also called brachytherapy or implant therapy, where a source of radioactivity is surgically placed inside the body near the tumor.

External radiation may also be called x-ray therapy, cobalt therapy, proton therapy, or intensity modulated radiation therapy (IMRT). This type of radiation is administered using a machine called a linear accelerator. Learn more about the steps involved in radiation therapy. Treatment can be given once or twice a day, depending on the treatment protocol being used. Treatments are given 5 days a week for several weeks, depending on the total final dose of radiation that is planned. Patients are given a break from treatment on weekend days to give normal cells some time to heal, thus reducing side effects. A person receiving external radiation therapy is not radioactive or dangerous to the people around him or her.

Internal radiation therapy places the source of the high-energy rays inside the body, as close as possible to the cancer cells. This may be done by implanting "seeds" (small pieces of the radioactive substance) or by using an implanted reservoir, into which a liquid radioactive substance is injected. This delivers very intense radiation to a small area of the body and limits the dose to normal tissue. Internal radiation therapy allows the doctor to give a higher total dose of radiation in a shorter time than is possible with external treatments. The radioactive substances used (also called the "radiation source") typically include radium, cesium, iodine, and phosphorus. Depending on the substance, the implant may be temporary or permanent, although the effect wears off over time in all cases. Depending on the type of radiation source, patients with radiation implants may need to be isolated from visitors for a period of time, so as not to expose others to radioactivity. Patients treated with temporary implants are not exposed to, and cannot expose others to radiation once the treatment is completed because the source has been removed.

What are the side effects of radiation therapy?

The doses of radiation used to destroy cancer cells can also hurt normal cells. Thus the side effects are directly related to the area of the body being treated. For instance, radiation that includes the abdomen can cause diarrhea because of the radiation's effect on the wall of the bowel. While side effects are unpleasant, there are treatments to help deal with them, and most side effects are temporary, disappearing gradually after therapy is complete.

Most radiation oncologists see their patients at least once a week while the patients are receiving treatment. This visit with the healthcare team serves as an opportunity to ask questions, discuss any side effects, and implement and necessary interventions to help relieve the side effects.

The following list includes some of the most common side effects of radiation therapy, but remember, these vary depending on the area being treated and each individual's reaction to therapy. Check with your radiation oncologist and health care team for more details on your specific situation. If side effects become severe, treatment may be put on hold to allow the tissue time to heal before continuing.

Skin reaction: There may be some reddening of the skin and the area may become irritated, dry, or sensitive. A skin reaction may progress to look like a sunburn. Treat the skin gently to avoid further irritation, and bathe carefully using only warm water and mild soap. Avoid perfumed or scented lotions or soaps, as these may cause further irritation.

Hair loss: Hair loss may occur in the area being treated. Loss of scalp hair occurs only if radiation is directed to the head. In some cases, this hair will not regrow after radtiaion. Hair that does grow back is often thinner. Hair regrowth will ultimately depend on the total radiation dose that is delivered.

Nutritional problems: Radiation can affect the membranes of the mouth and/or gastrointestinal tract, and can cause discomfort while swallowing, altered taste of foods, nausea, and diarrhea. Medications are available to treat nausea and diarrhea, and oral rinses and pain medicine may offer some relief for ulcers of the mucous membranes. Commercial mouthwashes should be avoided, since some contain irritating ingredients like alcohol. If this occurs, patients can try foods that are soft or soothing to the throat (such as ice cream or water ice).

Fatigue: Fatigue or weakness is one of the most common side effects of radiation therapy. Patients are not restricted from normal activity during radiation therapy, and many continue to work while undergoing treatment. However, they should balance normal activity with periods of rest, as needed. Fatigue usually resolves within several weeks after the end of treatment, but may last longer depending on the patients overall medical condition and whether or not they receive other cancer treatments after the radiation is complete.

Neutropenia: A neutrophil is a type of white blood cell that is important in fighting infection. While receiving radiation treatments, the body's number of neutrophils may be decreased, which is called neutropenia. This puts the patient at a higher risk of getting infections. Patients and those around them should wash their hands frequently to decrease the risk of getting an infection. Patients should avoid large crowds or people who are sick (i.e.: have colds). Patients should let their doctor or nurse know right away if they have a fever (temperature greater than 100.4), sore throat or cold, or a sore that doesn't heal.

These side effects are considered acute or short-term side effects because they occur during treatment and tend to resolve within a few months of the completion of therapy. With many therapies, including radiation, there is also a risk of long-term complications. These are problems that arise 5, 10, or more years after a treatment. In the case of radiation, long-term side effects are generally closely related to the area that was irradiated, and include: memory impairment; confusion; personality changes (all with brain irradiation); development of another cancer as a result of damage to tissue; cataracts; dental problems; heart problems (high blood pressure, high cholesterol levels); infertility; and hypothyroidism. Patients should talk with their healthcare team about their specific risks, and how these weigh against the benefits of treatment.

How will I know if radiation is working for me?

This answer varies, depending on the type of cancer being treated. Many patients will have radiology studies (CT scans, MRI scans, PET scans) periodically to see if the tumor has responded (shrunk, stayed the same, or grown). Some types of tumors are able to measured in the blood with a "tumor marker". This is a substance that is either produced by the tumor or by the body in response to the tumor, and can be measured by a blood test. If the chemotherapy is working, one would expect the tumor marker to decrease. In some cases, a decrease in a patient's symptoms may be able to signal if the medications are shrinking the tumor or not. Talk with your doctor or nurse about how your response will be measured.